The invention relates to telescopes, and more particularly relates to optical telescopes that are capable of operation in the visible and near-infrared portions of the electromagnetic spectrum. In its most immediate sense, the invention relates to optical telescopes and optical telescope arrays that are suitable for use in spacecraft (such as satellites) and other remote sensing applications.
Universities use nanosatellites for research in astronomy, climatology, and earth science. And, use of nanosatellites for both commercial and governmental purposes has been contemplated. For example, a nanosatellite network could be used to monitor the entire length of a pipeline in order to prevent oil or gasoline thefts by detecting persons who bring unauthorized truck-sized vehicles in the pipeline's vicinity. Alternatively, nanosatellites can be used for e.g. border control (monitoring aircraft that may be transporting drugs, monitoring movements of guerrillas) or prevention of environmental disasters (such as international fires in large extensions of protected forests).
An optical telescope intended for use in a spacecraft such as a nanosatellite must meet demanding constraints. It must be small, light, well-balanced, and mechanically robust. It must also be easily customizable; some nanosatellite applications will require a wide field of view, while others will require high resolution images, and still others will require the ability to acquire spectroscopic data or polarimetry data.
Therefore, objects of the invention are to provide an optical telescope and an optical telescope array for use in spacecraft and remote sensing applications such as nanosatellites, which telescope and array are small, light, well-balanced, mechanically robust, and easily customizable.
Conventional catadioptric optical telescopes of the Maksutov-Cassegrain type have excellent mechanical features; they are small, light, well-balanced, and mechanically robust. However, when used at wavelengths of between 400 and 1000 nm (visible to near-infrared radiation, which are required for nanosatellite applications) they have unacceptable levels of astigmatism, coma, and color spherical aberrations. And customizing a conventional Maksutov-Cassegrain telescope to meet the requirements of different nanosatellite applications would be quite difficult.
The invention proceeds from two realizations. The first of these is the realization that if a conventional Maksutov-Cassegrain telescope design is modified to employ second-surface reflection for the primary mirror and the secondary spot mirror (instead of first-surface reflection, which is conventional) the optical aberrations of the original design can be brought within acceptable limits while still preserving its advantageous features insofar as size, weight, balance, and robust character are concerned.
The second realization is that by using a binocular array made up of two telescopes having such a modified design, customization can be accomplished easily and inexpensively. This can be done by changing the orientation of the telescopes with respect to each other, changing the coatings on the lenses, and changing the filters that are used. If for example the telescopes are parallel with each other so that their fields of view coincide to be the same at the intended distance from the satellite, a high-resolution image can be obtained. Alternatively, if an image of a large area is desired, the telescopes can be precisely disinclined so that the fields of view at the intended distance are non-overlapping. Acquisition of spectroscopic and polarimetry data can be accomplished by using suitable coatings on the lenses and suitable filters, and it is possible to acquire both image data and spectroscopic or polarimetry data by configuring one telescope to acquire an image while configuring the other to acquire the non-image data desired.